Sciencemadness Discussion Board

Polylactic acid hydrolysis to lactic acid?

Ioxoi - 7-11-2008 at 14:31

I'm not sure if the rest of you have access to this, but in the lunchroom of a local restaurant they have "ECO-PRODUCTS" "made-from-plants" forks, knives and spoons and I am fairly certain they are polylactic acid. I've been a bit of an eco-terrorist and I've been swiping one or two every time I go.

I was thinking of making lactic acid with them. Granted, lactic acid isn't a terribly exciting or useful chemical, but just for the ease with which I can get these utensils it seems like a good idea to use them for some "reagent acquisition." :)

Polylactic acid is an ester polymer (COOH on one end condenses with the OH on the other end of the molecule). I figure either acid hydrolysis or attack with NaOH would be best, seeing as it takes regular H2O months to break it down.

Attack with NaOH would make the Na salt. However, I'm more interested in the pure acid, so I'll try acid attack instead. (I believe the plastic is formed from both the (-) and (+) enantiomers of lactic acid, so I will get a mix of then two when I hydrolyze the stuff.)

Questions: I will probably try experimenting today or tomorrow and post whatever happens. What acid should I use? HCl or H2SO4? I'm leaning towards HCl because it can be evaporated off afterward. Any idea how concentrated? How fast does it go? I'm planning on trying room temp HCl first, and if that doesn't work I'll heat the stuff. If that doesn't work I'll just have to boil those spoons in 20% H2SO4. :)

Hope to post details in a couple days...

Klute - 7-11-2008 at 14:47

I think acid hydrolysis would require extended reflux (+24h) with a large excess of acid to open up the polymer. You might better be off doing a saponification (basic hydrolysis), and then acidify the salt obtained.

I guess both HCl and H2SO4 would do the trick, i would aim for 10-20% HCl and 20-30% H2SO4.

Ioxoi - 7-11-2008 at 15:13

Optimistic but unlikely: Would NaHCO3 work as well? I wish it would because it is much cheaper than NaOH, but I fear it's too weak a base. I also have 5% ammonia but that might suffer the same problem. K2CO3 is also on hand...

Ioxoi - 8-11-2008 at 16:52

Unfortunately, it would seem that my "polylactic acid" utensils were not actually made out of polylactic acid as I was told. They were made from essentially useless "Plastarch.":(